Cameras shake from being used while moving (e.g., in a vehicle), and also because people cannot hold a camera perfectly steady. Shaking causes blur in images captured with longer exposure times, and other undesirable effects in general.
To compensate for shaking, many cameras have built-in anti-shake (often referred to as image stabilization) systems. Such systems are particularly useful in scenarios such as to correct camera shake from an unsteady hand, or while capturing video in a moving car or boat, where higher frequency vibrations and other relative movements of the camera cannot be otherwise handled. In general, such anti-shake-enabled cameras have a planar imaging surface that is moved horizontally and/or vertically as needed to compensate for the camera's unsteady movements.
However, optical lens systems do not generally have their best focus on a planar imaging surface. For example, spherical lens systems tend to best focus on a roughly hemispherical surface, called the Petzval surface. Much of the complexity of lens design is in forcing the lens system to achieve best focus on a planar imaging surface, far away from the Petzval surface.
Developments in sensor technology have yielded somewhat low resolution curved sensors (with the resolution likely to increase in the future) that provide for improved quality of images. However, with such curved sensors, existing anti-shake systems do not function correctly; indeed, such correction systems would instead make the captured images worse, (e.g., go in and out of focus).